Attached hereto is APPENDIX A, which contains the program listings for the preferred software modules for the programmable logic devices employed in an embodiment of the present invention. The contents of APPENDIX A are hereby incorporated by reference in its entirety.
1. Field of the Invention
The field of the present invention pertains to diagnostic x-ray imaging equipment. More particularly, the present invention pertains to real-time scanning-beam x-ray imaging systems and to devices incorporating a marker, such as a medical catheter incorporating an x-ray sensor, which allows the determination of the device""s precise position within another object.
2. Description of Related Art
Real-time x-ray imaging is increasingly being required by medical procedures as therapeutic technologies advance. For example, many electro-physiologic cardiac procedures, peripheral vascular procedures, PTCA procedures (percutaneous transluminal catheter angioplasty), urological procedures, and orthopedic procedures rely on real-time x-ray imaging. In addition, modern medical procedures often require the use of instruments, such as catheters, that are inserted into the human body. These medical procedures often require the ability to discern the exact location of instruments that are inserted within the human body, often in conjunction with an accurate image of the surrounding body through the use of x-ray imaging.
Current clinical real-time x-ray equipment produces high levels of x-ray exposure to both patients and attending staff. The United States Food and Drug Administration (F.D.A.) has reported anecdotal evidence of acute radiation sickness in patients, and concern among physicians of excessive occupational exposure. (Radiological Health Bulletin, Vol. XXVI, No. 8, August 1992).
A number of real-time x-ray imaging systems are known. These include fluoroscope-based systems where x-rays are projected into an object to be x-rayed and shadows caused by relatively x-ray opaque matter within the object are displayed on the fluoroscope located on the opposite side of the object from the x-ray source. Scanning x-ray tubes have been known in conjunction with the fluoroscopy art since at least the early 1950s. Moon, Amplifying and Intensifying the Fluoroscopic Image by means of a Scanning X-ray Tube, Science, Oct. 6, 1950, pp. 389-395.
Reverse-geometry scanning-beam x-ray imaging systems are also known. In such systems, an x-ray tube is employed to generate x-ray radiation. Within the x-ray tube, an electron beam is generated and focussed upon a small spot on the relatively large anode (transmission target) of the tube, inducing x-ray radiation emission from that spot. The electron beam is deflected (electromagnetically or electrostatically) in a raster scan pattern over the anode target. A small x-ray detector is placed at a distance from the anode target of the x-ray tube. The detector typically converts x-rays which strike it into an electrical signal in proportion to the detected x-ray flux. When an object is placed between the x-ray tube and the detector, x-rays are attenuated and scattered by the object in proportion to the x-ray density of the object. While the x-ray tube is in the scanning mode, the signal from the detector is inversely proportional to the x-ray density of the object
Examples of known reverse-geometry scanning-beam x-ray systems include those described in U.S. Pat. No. 3,949,229 to Albert; U.S. Pat. No. 4,032,737 to Albert; U.S. Pat. No. 4,057,745 to Albert; U.S. Pat. No. 4,144,457 to Albert; U.S. Pat. No. 4,149,076 to Albert; U.S. Pat. No. 4,196,351 to Albert; U.S. Pat. No. 4,259,582 to Albert; U.S. Pat. No. 4,259,583 to Albert; U.S. Pat. No. 4,288,697 to Albert; U.S. Pat. No. 4,321,473 to Albert; U.S. Pat. No. 4,323,779 to Albert; U.S. Pat. No. 4,465,540 to Albert; U.S. Pat. No. 4,519,092 to Albert; and U.S. Pat. No. 4,730,350 to Albert.
In a typical known embodiment of a reverse-geometry scanning-beam system, an output signal from the detector is applied to the z-axis (luminance) input of a video monitor. This signal modulates the brightness of the viewing screen. The x and y inputs to the video monitor are typically derived from the signal that effects deflection of the electron beam of the x-ray tube. Therefore, the luminance of a point on the viewing screen is inversely proportional to the absorption of x-rays passing from the source, through the object, to the detector.
Medical x-ray systems are usually operated at the lowest possible x-ray exposure level at the entrance of the patient that is consistent with the image quality requirement (particularly contrast resolution and spatial resolution requirements) for the procedure and the system. Typical patient entrance exposure in conventional 9xe2x80x3 filed of view image intensifier systems used in cardiac procedures, in the AP (anterior posterior) view with a standard adult chest, is approximately 2.0 to 2.8 R/min. The term xe2x80x9clow dosagexe2x80x9d used herein refers to a factor of 2 to 20 less than this.
Time and area distributions of x-ray flux follow a Poisson distribution and have an associated randomness which is unavoidable. The randomness is typically expressed as the standard deviation of the mean flux, and equals its square root. The signal-to-noise ratio of an x-ray image under these conditions is equal to the mean flux divided by the square root of the mean flux, i.e., for a mean flux of 100 photons, the noise is +/xe2x88x9210 photons, and the signal-to-noise ratio is 10.
Accordingly, the spatial resolution and the signal-to-noise ratio of x-ray images formed by known reverse-geometry scanning x-ray imaging systems are dependent, to a large extent, upon the size of the sensitive area of the detector. If the detector aperture is increased in area, more of the diverging rays are detected, effectively increasing sensitivity and improving the signal-to-noise ratio. At the same time, however, the larger detector aperture reduces attainable spatial resolution as the xe2x80x9cpixelxe2x80x9d size (measured at the plane of the object to be imaged) becomes larger. This is necessarily so because most objects to be imaged in medical applications (e.g., structures internal to the human body) are some distance from the x-ray source. In the known systems, therefore, the detector aperture size has been selected so as to effect a compromise between resolution and sensitivity, it not being previously possible to maximize both resolution and sensitivity simultaneously.
In the medical field, several conflicting factors, among them patient dosage, frame rate (the number of times per second that the object is scanned and the image refreshed), and resolution of the image of the object, often work to limit the usefulness of an x-ray imaging system. For example, a high x-ray flux may easily yield high resolution and a high frame rate, yet result in an unacceptably high x-ray dosage to the patient and attending staff.
Similarly, lower dosages may be achieved from the known systems at the cost of a low resolution image or an inadequate refresh rate. A preferred medical imaging system should provide low patient dosage, high resolution and an adequate refresh rate of up to at least about 15 images per second xe2x80x94all at the same time. Therefore, systems such as the known reverse-geometry scanning-beam x-ray imaging systems described above are not acceptable for diagnostic medical procedures where exposure times are relatively long and where, as is always the case with live patients, the x-ray dose received by the patient should be kept to a minimum.
Minimally invasive procedures in medicine are typically characterized by access to areas inside the body using existing orifices such as the ureter or by percutaneous entry such as a puncture of the femoral vein. In such procedures, various tools and catheters may than be progressed into the body and maneuvered using a real-time x-ray imaging for guidance. An estimated 3,000,000 medical procedures of this type were performed in 1993 under x-ray fluoroscopy guidance. Many of these procedures involve the introduction of a catheter into the coronary arteries and the heart, and the evaluation of cardiac function by inspection of images taken when contrast media is introduced via a lumen in the catheter. Some of the tools that may be inserted in this manner include lasers where the laser device is located outside the body and the laser light delivered to the site of interest with a fiber-optic wave guide disposed in a catheter, drug delivery systems adapted to deliver precisely measured quantities of a specific drug or radiological material to the site of interest, ultrasound, systems in which a transducer on the tip is used to view a site of interest by delivering the image over to a video system which can then display and record images of the site of interest, and other tools known to the art. It is also possible to adapt such procedures to non-medical applications where access is difficult and the value of the procedure high, e.g., engine diagnosis and repair.
As used herein, the term xe2x80x9cmaneuverable positionerxe2x80x9d is meant to collectively include and refer to, for example, catheters, probes, endoscopes, and other maneuverable positioners and tools.
The known medical x-ray imaging devices do not provide a highly-accurate determination of location for maneuverable positioners with a precise image of the patient""s internal structure. Generally, the physician using known systems can roughly ascertain the position of maneuverable positioners relative to body features within the patient, but precision and repeatability, the ability to return to the exact same place, especially in the axis parallel to the x-ray beam, is lacking. Thus the distance between the x-ray emitting source and the maneuverable positioner within the body may not be readily or accurately determined with the precision useful in today""s advanced medical procedures, which may require, among other things, the ability to determine a position with the maneuverable positioner, move the maneuverable positioner, and return the maneuverable positioner to the exact same place.
For example, since 1982 there has been increasing use of catheter ablation to cure certain types of arrhythmia. In these types of arrhythmia, such as Wolff-Parkinson-White syndrome, the conductive congenital muscle fibers can be made nonconductive by heating them locally to a sufficient temperature to cause scar tissue to form. Most of these ablations are done with radio-frequency energy but the emitting electrode must be placed within one to three millimeters of the muscle fiber location and it must stay in intimate contact with it for a number of heartbeats and respiratory cycles.
Although the treatment of arrhythmia through catheter ablation has some advantages, there are also some problems. The advantages of the procedure are that it has a very high success rate, it is minimally invasive, it can be performed in a few hours in a procedure room, and it is considerably less expensive than open chest surgery or a lifetime of drug therapy. The major disadvantage is that the length of the procedure is uncertain and typically long. This leads to difficulty in scheduling physicians and facilities, fatigue for both patient and staff, and high-radiation dosages for patient and physician.
Attempts to solve these problems have focused mainly on providing more steerable catheters to reduce the time to find the precise location of the ablation site and to position the catheter for remaining in contact with the substrate during the ablation time, which is typically five to ninety seconds, having more steerable catheters has not yet reduced the time or uncertainty of time because the location of the catheter is generally determined by looking at an x-ray image project on a monitor and by analyzing the electrocardiogram. Both of these actions must be done in real time in order to know whether to move the catheter and in which direction to move it. The actual direction of movement may be uncertain due to the nature of an x-ray image of soft tissue and blood, the poor control and feedback of the catheter, the movement of the heart, and the difficulty of determining direction from the electrocardiogram analysis.
In the U.S., there are currently 300,000 to 500,000 people who die each year due to arrhythmia that is a result of a myocardial infarction. However, it is believed that if the slow-conduction zone around the infarct could be electrically mapped and selectively ablated, that a cure could be obtained. Tests on animals and some humans have demonstrated the possibility of such a procedure but the success rate has been low. The reasons for the low success is thought to be the need to map the entire area of the infarct and slow conduction zone and then to be able to ablate multiple sites without depending on acquiring a characteristic electrogram once the ablation has begun. Current investigations attempting to solve the problem utilizing a catheter network array of nodes suffers from the problem of extracting the catheter network array from inside the heart without damaging the internal structure of the heart.
For various reasons, the imaging modalities of MRI, CT, and ultrasound are not normally suitable when anatomical markers are needed during cardiac diagnostic and treatment procedures. In addition, the use of known methods employing x-ray fluoroscopes for imaging typically has the serious disadvantage of not being able to distinguish anatomical detail inside the heart. The physician relies on the shadows generated, his or her intimate knowledge of the anatomy, the characteristic movement of the image and catheters caused by the cardiac cycle and the respiratory cycle, and for fine positioning, the electrocardiogram.
Accordingly, there is a need for devices and methods to provide a precise determination of the coordinates of a maneuverable positioner within a human patient during a medical procedure. The same techniques and apparatus can also be used to advantage in any x-ray procedure which requires accurate determination of the X, Y and Z coordinates of the position of a maneuverable positioner which may be adapted to sense x-rays.
An x-ray imaging system according to the present invention comprises a scanning-beam x-ray source and a multi-detector array. The output of the multi-detector array is input to an image reconstruction engine which combines the outputs of the multiple detectors over selected positions of the x-ray beam to generate a real-time x-ray image of the object.
An embodiment of an aspect of the invention includes an x-ray tube including a charged particle beam source and an anode target. Beam control circuitry focusses the charged particle beam and directs or scans the beam across the anode target in a predetermined pattern. For example, the predetermined pattern may be a raster scan pattern, a serpentine or xe2x80x9cSxe2x80x9d shaped pattern, a spiral pattern, a random pattern, a guassian distribution pattern centered on a predetermined point of the anode or such other pattern as may be useful to the task at hand.
A collimating element, preferably in the form of a grid, may be interposed between the x-ray tube and an object to be x-rayed. In one preferred embodiment, the collimating element is composed of a round metal plate having a diameter of about 25.4 cm (10 in) and includes a staggered array of apertures numbering 500 to 500 at the center row and column of the collimating element. The collimating element is preferably placed immediately in front of the emitting face of the x-ray tube. Other collimating element configurations may also be used. In one preferred embodiment, each of the apertures in the collimating element is constructed so that each of the axes of each of the apertures is directed toward (or points at) a detection point, e.g., the center of a multi-detector array, located a selected distance from the collimating element. That distance is selected to allow placement of the object to be x-ray between the collimating element and the multi-detector array. In the preferred embodiment, the function of the collimating element is to form thin pencil beams of x-rays, all directed from a focal spot on the anode target of the x-ray tube toward the multi-detector array.
A multi-detector array, preferably containing an array of detector elements (preferably an area array such as a DETx by DETy rectangle or square, or, more preferably, a pseudo-round array), is centered at the detection point. The multi-detector array preferably comprises a plurality of densely packed x-ray detectors. The multi-detector array is designed, positioned and applied, according to the present invention, in a manner that yields high sensitivity without loss of resolution. This results in an x-ray system having a resolution comparable to or better than that of known conventional x-ray systems at an exposure at least an order of magnitude less than that of the known x-ray systems. This aspect of the present invention provides important benefits in medical and other applications. X-ray dosage to patients and attending medical staff is reduced when using this aspect to perform current medical procedures. Procedures now believed to have too high a radiation exposure risk may become acceptable.
The output of the multi-detector array is preferably an intensity value for each detector of the multi-detector array for each x-ray beam emitted through an aperture in the collimating element. Because each aperture is located at a different point in space relative to the multi-detector array and the object under investigation, different outputs will be available from each detector of the multi-detectors array for each aperture that the x-ray beam travels through. The multi-detector array output may be converted into an image in a number of ways.
The imaging system of the present invention is also capable of use in stereo imaging. In one embodiment, the collimation element contains two groups of apertures. For stereo imaging, the axes of one group of apertures is constructed to point to a first detection point on a first multi-detector array and the axes of a second group of apertures is constructed to point to a second detection point on a second multi-detector array. By constructing two images form the outputs of the multi-detector array and using conventional stereoscopic display methods, a stereo image may be produced.
An imaging system of the present invention is also capable of highlighted imaging of materials which exhibit different x-ray transmissivities at different x-ray photon energies. Accordingly, for example, microcalcification, which is associated with approximately 60% of the breast cancer diagnosed, may be imaged. Calcium is also typically associated with heart disease when found in the coronary arteries. In one embodiment, by constructing the collimation element and/or anode target to sequentially emit two or more groups of x-rays beams each having different x-ray energy spectra and directing each group to the multi-detector array (more than one multi-detector arrays could also be used), the difference of transmissivities of the object under investigation at the various x-ray photon energies can be used to create an image, thus highlighting only those materials within the object under investigation which exhibit differential x-ray transmissivity. Optimized for the detection of calcium, for example, such an imaging system is a powerful tool for use in the early detection of breast cancer and other anomalies.
Utilizing a multi-detector array which intercepts the entire x-ray beam emitted from each aperture of the collimator element and image processing the array output is the preferred embodiment of the detector. It provides a maximum sensitivity without sacrificing the resolution provided by using a single small area detector. While a single detector of the same area as the multi-detector array would provide the same sensitivity, it would do so at the cost of a loss of resolution.
Additionally, sampling techniques utilizing information from less than a 1:1 image pixel to aperture ratio may be used for generating data from the multi-detector array which can reduce the complexity of the system, required processing speed, and energy consumption while providing virtually the same image quality.
An aspect of the present invention can also be used to identify the unique location of a marker transported within another object by a maneuverable positioner. In its most general sense, this would be accomplished by an x-ray sensitive marker disposed in a body and includes the transmission of an indication of the present of x-ray radiation outside of the body in which it is disposed.
According to one embodiment of this aspect of the invention useful in medical applications, a catheter comprises an elongated body having a distal end adapted to be inserted into a body cavity, blood vessel, digestive tract, or the like and a proximal end available to a person performing a medical procedure. The catheter includes at least one lumen running therethrough. An optical fiber is disposed in the lumen and extends from the distal end to the proximal thereof. A miniaturized (xe2x80x9cminixe2x80x9d) x-ray sensor comprised of an x-ray sensitive material is disposed at the end of the optical fiber positioned at the distal end of the catheter. The end of the optical fiber at the proximal end of the catheter is coupled to a photodetector. The reaction of the sensor material of the mini x-ray sensor to an x-ray beam sequentially transmitted through a collimator, coupled with the transmission of that reaction to the photodetector, allows the determination of the precise position of the sensor material. Embodiments of the techniques to determine this precise position from the mini x-ray sensor reaction is discussed in detail below.
Another aspect of the present invention is the ability to determine the distance of a maneuverable positioner containing a mini x-ray sensor from a known reference plane. Each x-ray beam emitted through a collimation grid aperture of the present invention is shaped like a diverging cone with its apex at the anode target and its divergence angle determined by electron beam spot size on the anode target and the geometry of the collimation grid apertures with respect to the anode target. The divergent beams are designed to overlap more and more the farther you get from the x-ray source. The mini x-ray sensor in this aspect is preferably disposed in a maneuverable positioner and may have (but is not required to have) a size smaller than the spacing between the apertures of the collimation grid. When such a sensor is disposed in the x-ray field it will detect, during a complete scan cycle, x-rays from only a certain number of apertures, the number depending upon the mini x-ray sensor""s distance from the output face of the collimation grid. When the mini x-ray sensor is located close to the output face of the collimation grid, it will react to x-ray pulses from a first number of apertures per scan cycle. At a greater distance from the output face, it will react to x-ray pulses from a second number of apertures greater than the first number. When the mini x-ray sensor is near the x-ray multi-detector array, it will react to x-ray pulses from an even greater number of apertures per scan cycle. By calibrating the number of apertures per scan cycle to which the mini x-ray sensors reacts with the mini x-ray sensor""s distance from a known reference, the distance of the mini x-ray sensor from the reference may be determined by consulting a look-up table and/or by interpolation.
When used as described herein, the above-described embodiment of the present invention answers the long felt need for anatomical markers during cardiac diagnostic and treatment procedures. Since typical reference positions for electrocardiograms are the high right atrium, the bundle of HIS, the apex of the right ventricle, and the coronary sinus, there is an opportunity to have at least three points located in the x-ray image during the cardiac cycle. These three points can precisely locate the coordinates of the ablation catheter. Knowing the coordinates of these points, the physician can then map an area with the catheter and correlate its position with the electrocardiograms. He can then return to the same spot after leaving it and can measure bounce or other movement, he can also measure internal dimensions of the heart mapping points, determine wall thicknesses, build 3D images from the data and overlay cardiac action potentials. In addition, in a subsequent procedure the same locations may be found from overlaying the maps of anatomy and cardiac potentials.
The initial work performed with this aspect of the invention was to analyze the images from a biplane x-ray system when it was gated to the cardiac cycle. In some cases this positioning using image analysis is adequate but the precision can be greatly improved if an x-ray marker is included in the catheter. With conventional image intensifier technology, such a point sensor would not be useful since the entire field of view is irradiated simultaneously. However, in a scanning-beam x-ray system, the beam irradiates only a small field of view at a given time and therefore the location of the sensor in each individual catheter can be uniquely identified. By utilizing a stereo or biplane scanning-beam system, the sensor can be located in three dimensions provided that the two beams are synchronized. The advantage of the above described medical catheter embodiment of the invention is that is permits existing catheters inside the patient to now also function as anatomical markers when a mini x-ray sensor is employed, significantly reducing the time to map and ablate. Additional advantages are more detailed mapping of the cardiac substrate, correlation of the intercardiac electrodes with anatomical location, display in three dimensions of the intercardiac electrodes on an image of the heart, and comparison of electrograms from studies done at different times by overlaying.
It is an object of one aspect of the present invention to provide a scanning-beam x-ray imaging system capable of use in medical diagnostic procedures undertaken on living human patients.
It is also an object of another aspect of the present invention to provide a scanning-beam x-ray imaging system which provides high resolution images at adequate frame rates while minimally exposing the object under investigation to x-ray radiation.
It is a further object of another aspect of the present invention to provide a scanning-beam x-ray imaging system having improved resolution at a distance from the plane of the source of the x-rays while maintaining decreased x-ray flux levels.
It is also a further object of an aspect of the present invention to provide a method and apparatus for precisely determining the position of a maneuverable positioner within an object undergoing an x-ray procedure.
It is yet a further object of an aspect of the present invention to provide a method and apparatus for precisely and simultaneously determining and displaying information related to the X, Y and Z coordinates of a maneuverable positioner within an object undergoing an x-ray procedure.
It is also a further object of an aspect of the present invention to provide an electronic glove and other improvements in safety for medical applications by feedback of position from a mini x-ray sensor.
it is an object of another aspect of the present invention to provide for improved image quality by employing region of interest scanning.
It is a further object of an aspect of the present invention to provide a scanning beam x-ray imaging system for non-medical applications where scatter may degrade image quality, e.g., to image or inspect honeycomb airplane structures, corrosion, and printed circuit boards.
An advantage of an aspect of the present invention is that it can provide a method and apparatus for generating a xe2x80x9croad map.xe2x80x9d For example, once a maneuverable positioner incorporating a mini x-ray sensor in accordance with the present invention has been threaded to a particular location of interest within the body or object, it can be removed and then re-threaded along the same path by generating waypoints, e.g., by determining X, Y and Z coordinates of various locations passed through during the first insertion. These waypoints may be obtained as frequently as desired along the first path taken to the location of interest to facilitate retracing the same path on subsequent occasions. This aspect of the present invention may have important application in intravascular and intracardiac ultra sound procedures.
Another advantage of an aspect of the present invention is that it can provide a method and apparatus to precisely locate and monitor the shape or position of stents. The precise location of the surface of a stent can be obtained through use of an x-ray sensing maneuverable positioner in accordance with the present invention by defining points along the surface of the stent, determining the X, Y and Z coordinates of those points and recording them. Subsequently, X, Y, and Z coordinates for those defined points can be redetermined and recorded over time and changes in shape or position of the stent can be observed and plotted.
Another advantage of an aspect of the present invention is that it can provide a method and apparatus for repeatable delivery of drugs, radiologic and similar materials to a specific site in the body.
These and many other objects and advantages of the present invention will become apparent to those of ordinary skill in the art from a consideration of the drawings and the description of the invention contained herein. The principles of the present invention may be employed in any application, medical or industrial. Principles or aspects of the present invention can be applied for example where location of internal features of an object is desired and insertion of an x-ray sensitive device is feasible. Industrial applications are variously called x-ray inspection, x-ray analysis, failure analysis, non-destructive testing, and in-situ testing.